The present invention relates to well apparatus and, in particular, to underwater apparatus for running a casing string into the well bore, cementing the casing string in place, and sealing the annular seal region between a casing hanger body and the surrounding wellhead bore.
In the drilling of oil and gas wells at an underwater location, a casing string is run into a well bore, and supported by a hanger body resting on complementary seats within a surrounding wellhead. After the casing string is cemented in place, a suitable seal assembly, referred to as a packoff assembly, is actuated (energized) to packoff (seal) the annular seal region between the exterior of the hanger body and the surrounding wellhead. Apparatus for performing the above method is illustrated in a number of U.S. Patents, such as, for example, U.S. Pat. Nos. 3,468,558, 3,468,559, 3,489,436, 3,492,026, and 3,871,449.
In such apparatus, the casing hanger body and packoff assembly are lowered into position at the same time on a running tool. In some of the above apparatus, the packoff assembly is lowered into position initially connected to the casing hanger, while in other apparatus, such as shown in U.S. Pat. No. 3,871,449, the packoff assembly is not connected initially to the hanger body, but is supported above the hanger body through an intermediary device which is responsive to actuation by the running tool. After the hanger body and packoff assembly have landed within the wellhead, and after cementing has taken place, the running tool is released from the hanger body which also actuates the intermediary device(s) permitting the packoff assembly to move downwardly toward the hanger body and then into the annular seal region between the exterior of the hanger body and the interior of the surrounding wellhead. The packing seal portion of the assembly is then energized to packoff (seal) this annular seal region.
In one apparatus, as disclosed in the U.S. Pat. No. 3,871,449, movement of the packoff assembly into threaded engagement with the hanger body is accomplished by actuation of a spring where rotation of the running tool energizes the packoff assembly. In another apparatus, as shown in the U.S. Pat. No. 3,924,678, energization is accomplished by hydraulic fluid operating on a running and setting tool, and then a locking device is used to lock the packoff seal in place. See also U.S. Pat. No. 3,933,202 where weight is used to energize the packoff seal portion of the packoff assembly.
Reference is also made to U.S. Pat. No. 3,797,864 which discloses an axially deformable elastomeric packing.
This invention relates to that type of apparatus in which the packoff assembly is not connected to the hanger body initially, and is an improvement of such prior art by maintaining the packoff assembly above the casing hanger, then mechanically positively moving the packoff assembly downwardly during and after the running tool is released from the casing hanger. This entire operation--seating the casing hanger within the wellhead, cementing the casing hanger in place, packing off the seal region and pressure testing off the seal for leakage--is accomplished in one trip between the vessel and the well. It will be apparent that, with the separation of the packoff assembly and casing hanger, there is improved flowby through the seal region. It should also be apparent that still another feature of the invention is that it enables the casing hanger and running apparatus to be shorter than existing equipment.